Plant parasitic nematodes cause serious economic damage to many agricultural crops around the world. The nematodes in this group are microscopic worms and in general are obligate parasites of plants. They feed mostly on the roots of host plants; however, several genera are known to parasitize above-ground parts including stems, leaves and flowers as well.
Almost all the plant species of economic importance are susceptible to infection by some species of nematodes (notable exceptions are marigolds and asparagus). For example, root knot nematodes (RKN), (Meloidogyne spp.) are capable of parasitizing more than 3,000 species of crop plants. These plants include agronomic crops, vegetable crops, fruit trees, flowering trees and shrubs. Nematodes reportedly cause crop losses worth more than six billion dollars in the United States alone and more than one hundred billion dollars around the world.
The symptoms due to parasitic nematode injury vary widely depending on the plant host, the nematode species, the age of the plant, the geographical location and climatic and external environmental conditions. In general, an overall patchy appearance of plants in a field is considered to be indicative of nematode infestation. More specifically, nematode injury results in galling of the roots (abnormal swelling in the tissue due to rapid multiplication of cells in the cortical region) caused by species of root knot (Meloidogyne spp.) and cyst (Heterodera spp.) nematodes, lesions (localized, discolored areas) caused by lesion nematodes (Pratylenchus spp.), suppression of cell division resulting in stubby roots (Trichodorus spp.), growth abnormalities including crinkling or twisting of above-ground parts (Aphelenchoides spp.), and even cell necrosis (death) in some cases. Plant parasitic nematodes may be endoparasitic in nature, as in the case of the root knot and lesion nematodes, or ectoparasitic as in the dagger nematode (Xiphinema spp.) and lance nematode (Hoplolaimus spp.). Nematodes can be vectors of plant viruses and are also known to induce disease complexes, predisposing plants to infection by other plant pathogenic fungi and bacteria.
Chemical nematicides, either soil fumigants or non-fumigants, have been in use for many years and are among the few feasible options for countering nematodes. At present, repeated applications of synthetic chemicals to the field are required prior to planting the crop. These chemicals are extremely toxic to non-target organisms besides nematodes and many of them may pose serious threats to the environment. With the emphasis on clean water and air by environmental groups and governmental agencies and the detection of many of these active ingredients or the metabolites thereof in ground water and several non-target organisms, there has been serious concern as to the wisdom of continuing the use of these chemicals. One of the most effective, economical, and widely used nematicides, DBCP (1,2-dibromo-3-chloropropane), found in ground water has been judged to induce male sterility and possible carcinogenesis. Another widely used chemical, EDB (ethylene dibromide), has also been found in ground water.
Another very common insecticide-nematicide, aldicarb (2-methyl-2-(methylthio)-propionaldehyde-o-(methylcarbamoyl)oxime), has been found to have high acute toxicity. Aldicarb has been found in ground water in several regions of United States. 1,3-D (1,3-dichlorpropene), yet another commonly used soil fumigant and nematicide, is identified as a probable carcinogen. The US EPA recently revoked all tolerances for residues of carbofuran (2,3-dihydro-2,2-dimethyl-7-benzofuranyl methylcarbamate) on crops and cancelled some product registrations after determining that the risk from aggregate exposure does not meet their safety standard. The recent decision by the EPA to limit and eventually discontinue the use of the soil fumigant, methyl bromide, for agricultural purposes, including it's effect as a nematicide, presents a threat to the efficiency and quality of agricultural production in the United States.
Natural products such as N-acetyl-D-glucosamine, which may be derived from microorganisms and which are the waste products of industrial fermentation processes, have been disclosed as nematicidal in U.S. Pat. No. 5,057,141.
Biopesticides have been developed as an alternative to chemical pesticides. They are obtained by fermentation and can be used either as a crude biomass or purified. Typically, fermentation is carried out at temperatures in the range of 20-40° C. For example, submerged fermentation at 28-30° C. of Paecilomyces fumosoroues fungal isolate ATCC No. 20874 produces a fungal biomass for control of nematode infestation as disclosed in U.S. Pat. No. 5,360,607; whole fermentation broth from fermentation at 28° C. of Streptomyces thermoarchaensis NCIB 12015 is disclosed as nematocidal in U.S. Pat. No. 5,182,207; broth obtained from fermentation of Streptomyces cyaneogriseus noncyanogenus NRRL 15773 at 28° C. is effective against nematodes as disclosed in U.S. Pat. No. 5,439,934; and broth obtained by fermentation of the fungus Myrothecium verrucaria at temperatures 25 to 30° C. is disclosed as nematicidal in U.S. Pat. No. 5,051,255.
However, there is still a need for the development of new and effective nematicides. Plants were suggested as a source of effective pesticidal compounds as many plant essential oils exhibit antimicrobial, insecticidal, fungicidal and herbicidal activity. They have been applied as pesticides for pest, disease and weed management.
Certain plant essential oils have been evaluated by the USEPA and have been determined to qualify for an exemption from registration as minimum risk pesticides and are listed in 40 C.F.R. §152.25 (b). However, high volatility, phytotoxicity and low water solubility of some oils have limited their use in crop protection.
One plant essential oil used in agricultural applications is ProGuard® 30% Cinnamaldehyde Flowable Insecticide, Miticide and Fungicide (U.S. Pat. Nos. 6,750,256 B1 and 6,251,951 B1). However, a disadvantage of this commercial product is that it contains the chemical preservative o-phenylphenol.
Nematicidal activity of plant essential oils was reported, among others, by Y. Oka (Nematology, Vol. 3(2), pp. 159-164, 2001) and R. Pandey (J. Phytopathology 148, 501-502 (2000)). Essential oils of some plants and their components have been tested for nematicidal activity in vitro and in soil. Some plant essential oils, which were determined to have nematicidal activity, include essential oils of apple mint (Mentha rotundifolia), caraway (Carum carvi), fennel (Foeniculum vulgare), oregano (Origanum vulgare), Syrian oregano (Origanum syriacum), and wild thyme (Coridothymus capitatus). Also, it was reported that aromatic and aliphatic aldehydes, including cinnamic aldehyde (also known as cinnamaldehyde) possess strong nematicidal activity in vitro. For example, U.S. Pat. No. 6,251,951 B1 demonstrates that cinnamaldehyde has nematicidal activity in the presence of a 2% Tween 80 and 6% NaHCO3 vehicle.
U.S. Pat. No. 6,231,865 B1 describes a synergistic effect when garlic oil or extract is combined with essential oils, which results in an improved insecticide/fungicide activity. Garlic extract is defined in this patent as any liquid removed from cloves of garlic and may include garlic oil and water. The preferred essential oil in the mixture was claimed to be cottonseed oil, and/or cinnamon oil. Sodium lauryl sulfate was used at 10% to emulsify the garlic extract. No attempt was made to describe or quantify the actual composition of garlic juice. Constituents in the garlic juice may vary substantially depending upon the source of garlic and method of extraction. Nematicidal activity with the garlic juice is, however, not described.
WO/2006/109028 “A Pesticide and Repellent” describes the use of garlic liquid concentrate as an insecticide, nematicide and molluscocide. Garlic concentrate was shown to have the properties associated with garlic oil/fresh garlic extract in terms of its repellency to various life forms and its action as a pesticide, but it does not require the distillation stage involved in the isolation of the garlic oil and is stable to long term storage without a decrease in the activity of the material. Allyl poly-sulphides, the active components resulting from decomposition of allicin in the garlic liquid concentrate were shown to be in the range 2 to 4% wt./wt. This published patent application also disclosed that diallyl sulphides of the formula RSR, RS2R, RS3R, and RS4R account for 66% (±10%) by weight of the total poly-sulphides present. These diallyl sulphides were determined to be present in the approximate ratio of 4-5%; 5-8%; 31-38%, and 19-22% by weight, respectively, of the total poly-sulphides present. The published patent application also disclosed a granular formulation of garlic concentrate impregnated onto wood flour with a binder. The granules (NEMguard) were successfully evaluated as nematicidal.
The nematicidal activity of the cinnamyl acetate component of oil from Cinnamomum verum and of diallyl disulphide and diallyl trisulphide from garlic (Allium sativum) was reported by Park et al, in 2005 (Nematology 7(5), 2005, 767-774). These were the most active essential oils from 43 plant species tested. The main components of the essential oils with nematicidal activity in the 2005 study were reported by Park et al, in 2002 (J. Pesti. Sci. 6, 2002, 271-278) to have insecticidal or acaricidal activity against five major arthropod pests. Diallyl disulphide and diallyl trisulphide from Allium were reported by Auger et al, (Agroindustria 3(3), 2004, 5-8) as having good activity against soil pathogenic fungi, insects and termites.
While both cinnamaldehyde and garlic extract are known in the literature for their nematicidal, insecticidal, fungicidal and miticidal activity, cinnamaldehyde may result in phytotoxicity to target plants especially when used at nematicidal rates (500 ppm and above). At concentrations of 300 ppm, nematicidal activity is only marginal. While at doses of 300 ppm and above, garlic extract may be effective in controlling nematodes, and exhibits no phytotoxicity, its cost per treated acre may be prohibitive.
Garlic extract used in earlier formulation studies is often aqueous based and the stability of active components in aqueous preparations is not well established. No prior art exists for formulations containing concentrated, dry powdered version of garlic extract (allicin) and cinnamaldehyde for effective and economic control of nematodes, fungal pathogens, insects and mites.
Accordingly, there is a need to develop safe, easy-to-use, cost effective delivery systems, so as to improve the biological effectiveness of plant essential oils/plant extracts, for agricultural applications.